Design and assessment of grid-driven distributed cogeneration

The increasing deployment of renewable energy sources into the power system will lead to larger fluctuations in electricity supply. Currently, these are balanced by pumped hydro and conventional fossil power plants. The electrification of transport and thermal energy supply of buildings will impose new loads to the electric distribution grids. These developments will occasionally lead to overproduction of power and grid overload caused by heat pumps and electric vehicles, e.g. in cold winter nights. Besides such electrical demand a significant heat demand caused by buildings needs to be efficiently supplied. A contribution to an efficient heat provision could come from cogeneration systems. Additionally, cogeneration units could be utilized as flexible, distributed power plants that offer reliable and fully controllable supply while mitigating load induced grid congestions in the electric distribution system. To serve the aforementioned purpose, time resolved states of the electric energy system need to be determined and transmitted to the co generators. Hence, a dynamic CO2 factor of the national power plant portfolio and the demand for congestion power in a corresponding local distribution grid need to be considered. Based on these status signals dynamic operation and control strategies are implemented. In addition to the operation, the performance of a grid-driven cogeneration system depends on its output capacity and the size of the thermal energy storage. However, sizing and control strategies are mutually dependent. Thus, both aspects are simultaneously considered with respect to an optimal design method. The performance assessment of cogeneration is conducted based on CO2 abatement cost and the potential for congestion management on distribution system level. The evaluation and optimization relies on dynamic simulation models coupled with a genetic optimization algorithm and is conducted for multiple building energy systems and boundary conditions. The systems’ boundary conditions are determined by renewable energy sources penetration scenarios, distribution grid topology and different technology shares (e.g. electric vehicle and heat pump). As a result, the optimal design under given boundary conditions is found and the influence of different factors like building application, power system context and control approach on the design and performance of the cogeneration system is analyzed. In this regard, general design implications are identified. To conclude the analysis an economic evaluation of cogeneration is conducted. An important measure in this context is the levelized cost of electricity for flexible power generation in comparison to conventional power plants. These serve as an indication for the marketing potential of grid-driven cogeneration in a given system context and signify the role of cogeneration in a future power system